The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-170268 filed on Apr. 30, 2001 the entire contents thereof is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a piston for an internal combustion engine. More particularly to a piston for an internal combustion engine suitable for high-speed revolution and miniaturization.
2. Description of Background Art
A conventional type piston provided with a crown, a piston pin boss integrated with the crown and a pair of skirts opposed includes a groove for a piston ring that is provided on the periphery of the crown is disclosed in Japanese Utility Model Publication No. Hei 7-7570. FIG. 6 shows such conventional type structure, a top ring groove 2, a second ring groove 3 and an oil ring groove 4 are provided on the periphery of a crown 1 and a piston ring not shown is fitted into each groove. A lubricator 5 that pierces the crown is formed at the bottom of the oil ring groove 4.
A piston pin boss 6 is provided having a skirt 7 with a lower end of the skirt 7 extending downwardly a greater distance relative to the lower end of the piston pin boss 6 and a part having a difference in a level 8 for a machining datum is formed.
In this disclosure, the upside and the downside of the piston are based upon states shown in FIGS. 6, 1, 3 and 4, and the upside, the downside, the right and the left in each drawing are equivalent to those of a product or a part equivalent to an embodiment.
As the weight is increased by the quantity when a lower part of the skirt 7 protrudes a longer distance downwardly as in the conventional type, the high-speed revolution and the miniaturization of an engine may be impaired. In case where the circumferential width of the skirt is large, a similar problem also occurs.
Also, in the case when lubrication is not enough even if a lubricator is provided at the bottom of the oil ring groove, the contact of the piston with a cylinder becomes strong, and scratching by the piston and seizure may occur.
Further, the part having a difference in a level 8 for a machining datum is provided in the lower part of the skirt 7. However, the part having a difference in a level 8 may cause a crack due to stress concentration under a condition in which the skirt 7 applies a large load. An object of the present invention is to provide a piston in which the above-mentioned problems are solved.
To solve the above problems, a piston for an internal combustion engine according to the present invention discloses a piston for an internal combustion engine provided with a crown, a pair of piston pin bosses respectively integrated with the crown and opposed and a pair of skirts respectively integrated with the crown and opposed thereto wherein the lower end of the skirt is located on the upside of the lower end of the piston pin boss.
The present invention includes a circumferential width of the skirt that is equivalent to 40% or less of the diameter of the piston.
The present invention includes first lubricators for piercing the crown from an oil ring groove provided on the circumferential side of the crown and second lubricators for piercing the skirt under the oil ring groove.
The present invention includes a part having a difference in a level for a machining datum that is removed from the lower end of the skirt.
According to the present invention, as the lower end of the skirt is located on the upside of the lower end of the piston pin boss, the area of the skirt can be minimized, as a result, as an increase in the weight by the skirt is prevented and lightening is possibly realized, an engine can be revolved at high speed and can be miniaturized. Each lower end of the skirt and the piston pin boss means the farthest part from the crown in the axial direction of the piston.
According to the present invention, as the ratio of the circumferential width of the skirt to the diameter of the piston is 40% or less, the area of the skirt can be minimized and the lightening and miniaturization are enabled.
According to the present invention, as the lubricator is provided under the oil ring groove, the skirt can be sufficiently lubricated. Therefore, the lubrication of the skirt can be stabilized.
According to the present invention, as the part having a difference in a level for a machining datum is cut from the lower end of the skirt, stress concentration under a condition in which a large load is applied is solved and the specification in which a crack is hardly caused can be set.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.